Orifice plates are mounted to ink-jet pens and include orifices through which ink drops are expelled by any one of a number of drop ejection systems. One such system is known as the thermal type and includes a thin-film resistor that is intermittently heated for vaporizing a portion of ink near an adjacent orifice. The rapid expansion of the ink vapor forces a drop of ink through the orifice. A partial vacuum or "back pressure" is maintained within the pen to keep ink from leaking out of the orifices when the drop ejection system is inactive.
There may be several orifices formed in a single orifice plate, each orifice having an associated drop ejection system for supplying a drop of ink on demand as the ink-jet pen scans across a printing medium.
Some of the ink that is ejected through the orifice does not reach the printing medium (such as paper), and instead collects on the outer surface of the orifice plate (that is, the surface facing the printing medium). Some of this residual ink accumulates or puddles adjacent to the edge of the orifice and may alter the trajectory of the subsequently ejected drops, thereby reducing the quality of the printed image.
Residual ink on the outer surface of the orifice plate also tends to trap stray particles, such as paper fibers. The fibers may be held by the ink near the orifice to partially block the orifice and interfere with ink drop ejections. Further, residual ink on the orifice plate outer surface may collect near the orifice into a thin sheet that is in fluid communication with ink stored in a supply chamber that is just inside the orifice. As a result, a continuous ink path between the chamber and the outer surface of the orifice plate may be formed. The path promotes ink leakage through the orifice. Accordingly, the outer surface of an ink-jet pen orifice plate should be designed so that ink does not puddle in the vicinity of the orifice nor accumulate on the plate in an amount that traps fibers and facilitates leakage as mentioned above.
The inner surface of an orifice plate is exposed to the supply of ink. The ink flows over the inner surface to each orifice. Preferably, the inner surface of the orifice plate, including the portion defining the orifice, should facilitate the flow of ink from the supply through the orifice so that the drop ejection system receives a continuous and uniform flow of ink.